The use of locks for slide fasteners on flexible money or security bags has long been established as indicated in the aforementioned patents. The principle reason for using such a lock is to seal the bag against unauthorized opening or gaining access to the contents without such access being discernable. In situations where such locked bags are being transported by bonded messenger, unless the lock, slide or bag shows physical signs of opening, insurance coverage may be disputed and disclaimed. More importantly, however, when private and confidential papers are being transported it may not be discovered whether unauthorized access has been obtained if the lock can be easily defeated such as by picking and then restored to its locked position. Thus, one of the requirements is that the lock should be of sufficiently high security that it is not easily picked or otherwise defeated.
In general, the basic structure of bag locks has remained the same over the years. It consists of a housing that is adapted to be fixed to the bag adjacent the end opening where the slide fastener reaches a closed position with the housing presenting an anvil portion underlying the zipper slide and a rotatable lever or keeper which carries the lock mechanism and is adapted to either overlie the anvil to confine the slide or to swing out of the way to release the slide for opening the bag. In one of the earlier versions as described in the Hart U.S. Pat. No. 3,070,986, the lock tumblers were the sole means for preventing the turning of the keeper arm. While it possessed one desirable advantage of enabling the removal of the key with the keeper in the open position and automatic locking upon shifting the keeper to the slide confining position, the lock itself was easily defeated. Indeed, it was not uncommon for such locks to simply pop open upon impact especially when dropped through a deposit chute since the lock structure weight at the one end of the bag tends to lead downward for impact at the bottom of the chute.
In subsequent approaches to overcome the afoementioned problems, such as in U.S. Pat. Nos. 3,580,016, 3,653,236 and 3,785,185, pop-up type keeper arms were employed which enabled inter-engaging elements of the keeper and housing in the closed position to protect the tumblers against any torque that may be applied to the keeper. One such arrangement, as shown in U.S. Pat. No. 3,653,236 even contemplated use of an axial pin tumbler type lock for greater pick resistant security. However, the pop-up type handle required a somewhat larger housing to allow for the relative axial movement of the keeper and additional mechanical locking mechanism was required. This added significantly to the massiveness of the lock as well as increasing the cost of manufacture.
One attempt to overcome the disadvantages of the pop-up type lock and return to the rotatable but fixed axially movable keeper arm is presented in U.S. Pat. No. 4,019,353. There, a lock bolt mechanism which is spring pressed is coupled to the lock cylinder and the bolt can be moved to free the handle for rotation or automatically be restored upon rotation of the keeper arm to the closed position. Again, the mechanism involved is such that possible operational difficulties may be encountered together with assembly problems and manufacturing costs involved.